Testing device for search units of flaw detectors



April 12, 193.8.

TESTING DEVICEFOR SEARCH UNITS OF FLAW- DETECTORS Filed Oct. 27, 1955 I 2 Sheets-Sheet 1 10 WA IFIER 2 0 a d; x 5

1 I inventor Lam-Ami DELA/VTY Agril 12, 1938. L. J. DE LANTY 2,113,783 I TESTING DEVICE FOR SEARCH UNITS OF FLAW DETECTORS L Fi led Oct. 27, 1935 2 s eet -sheet 2- llll l llIlllll-- I I E ,BIJIIH1;61IIHIHII g g I I IIIIIIIL I 6 Zinnentorattorney l'io utilized in testing the coils.

' Patented Apr. 12, 1938 PATENT OFFICE TESTING DEVICE-FOR SEARCH UNITS OF FLAW DETECTORS Loren J. De Lanty, Spring to Sperry Products,

Valley, N. Y., assignor Inc., Brooklyn, N. Y., a

corporation of New York Application October 27, 1933, Serial No. 695,494

3 Claims. This invention relates' to a method of, and

means for, testing the searching units of flaw detector mechanisms of the type employedin the Sperry. rail flaw detector cars. It isnow wellknown that the principle employed by the Sperry flaw detector cars is the movement of a plurality oi coils in constant space relation to a conductor through which current is passed. If the conductor is of homogeneous structure .the coils will'cut a constantly equal number or lines of force surrounding the conductor and no E. M. F. will be generated. However, when a region of flaw is encountered, the electromagnetic field surrounding the conductor in that region is distorted from normal and the coils will cut a different number of lines of force on entering the said'region, and

- this variation in the number of lines or force out by the coils will generate an E. M. F. in the coils, which, after beingsuitably amplified, may be caused to operate an indicator such as a recorder.

The above method depends upon the perfection of the coil formation, for, should the coil become externally shorted, totally or partially, as by a resistance due to dirt across the terminals of 5. the coil, or should the circuit through the coil be completely broken, or should even a certain number of turns of said coil become internally shorted, as by breakdown of the insulating medium between turns of the coil, then obviously an error 'is introduced and the detector system is either partially or wholly rendered inoperative by reduction of the voltage output 01 the coil aiiected, orhy electrical unbalance of the pair 0 coils containing the affected coil. l 5 The detector coils comprising the search unit are enclosed in various enclosing means depending upon the type of search unit employed. Thus the coils, may be contained in Bakelite or in metallic, non-magnetic casings. It-is the principal purpose of my invention to provide a means whereby the electrical excellence of theiarching coils may be readily detected by a suitable testing means without dismantling the coil from its casing/or the casing from its mounting. For this purpose I utilize the broad principle of creating and causing the tested coil or coils to vary an oscillatory circuit.

Further objects and advantages 01' my inven-' 'tlon will become apparent in thefollowing de-' tailed descriptian thereoi'. I

In the accompanying drawings,

Fig. 1 'is a side elevation of a portion of a Sperry rail flaw detector carQshowing a portion 01' the mechanism applied thereto which is Fig. 2 is a wiring diagram illustrating the principle of testing embodied in this invention.

Fig. 3 is a view of one 01' the elements of the searching unit of Fig. 1, showing the relative positioning of the coils of Fig. 2 in juxtaposition to establish the oscillatory circuit. I

Fig. 4 is a view similar to Fig. 2, showing another application of the same testing principle.

Fig. 5 is a wiring diagram of a modified form showing a modification'o'f my testing device.

Fig. 6 is a view similar to Fig. 1, showing another application of the same testing principle.

- Fig. '7 is a portion of a wiring diagram showing a modified principle of testing.

' Fig. 8 is a wiring diagram, similar to a portion of Fig. 5, showing an alternative method of compensating for variations in resistance.

Referring to Fig. l, I have shown a portion of a Sperry rail flaw detector car having a car body l0 adapted to travel over rails II. Flaws within the rail are detected by means of detector coils which, in this instance, are shown as enclosed in drum casings l2, said coils forming a search unit supported upon a detector carriage l3, adapted to ride on the rails by means such as rollers it. The detector carriage is in turn supported upon the current brush carriage 20, which is adapted to ride on the rails by means such as rollers 2| and is provided with current brushes 22, 23 for. leading current from a generator (not shown) within the car body into and out of the rail. Said current brush carriage 20 maybe raised to inoperative position by means such as springs (not shown) and cables 25, and may be lowered to operative position'i n engage- .ment with the rail by means such as fluid pressure pistonsfl, operating within, fiuid pressure cylinders 28, to which compressed fluid may be supplied. As the car travels over the rails the current supplied thereto creates an electromagnetic field surrounding the same, said field being uniform so long as the rail does not contain a Y flaw, but being distorted in the region of flaw. The said coils cut a constantly equal number .of' lines of force, as hereinbefore explained, except when entering and leaving a region of flaw, at

will have no resultant effect upon the pair of coils.

As shown in Fig. 1, each coil is enclosed within a cylinder which may be a metal casing from broken. In the form of invention shown in Fig.

2, I test a pair of coils at one time but it will be apparent from the following description that a single coil may be tested by the same method.

The testing method disclosed in Fig. 2 consists in establishing an oscillatory circuit and causing the detector coil under test to affect said circuit, of which it is a part, so as to produce a change in the conditions of oscillation. If there is no defect in the detector coil, or external load across the coil, a certain indication will be obtained upon a D. C. ammeter in the plate circ iit of the oscillator. If the detector coil is Opemcircuited, no oscillatory circuit is completed, the grid circuit so being opened. If the detector coil is otherwise defective, as described, the amplitude of oscillation will be either partially decreased or reduced to zero. Any such change in amplitude of oscillation from that obtained with a perfect coil is indicated by the D. C. ammeter', a smaller reading resulting when defects are present. Such internal defects as shortsor excessively low terminal resistance are so characteristically distinguished from opens, the latter resulting in a slowly increasing D.C. plate current, indicated by the ammeter, due to the opened grid of the oscillator. One means of establishing the oscillatory circuit is shown in Figs. 2 and 3.

In Fig. 3 I have shown one of the detector coils |2, mounted upon a core 30, and on the same core 30 I mount an auxiliary coil 3| in inductive relation to coil i2. A similar construction is to be found in each of the detector coil' casings.

It will be seen that the circuit through the detector coils l2 normally extends to an amplifier whose output operates an indicator. When thedetector coils are to be tested for. defects, all load therefore I provide means, in this instance, within the car body, whereby the circuit from the detector coils to the amplifier is broken and said the frame of detector carriage I3 as shown in Fig. 1.

It will be seen that when the contacts 5| and 52 are made and contacts 53 are broken; the output from the oscillator 40 extends from plate 43 through auxiliary coils 3|, which, by reason of inductive coupling to detector coils )2, establishes a feed-back into the grid 42 to set up the oscillation. The extent ofosciilation' may be read upon a direct current ammeter A. If detector Said circuit may comprise an ordinary the coil assembly'to be tested at will.

coils I! are in fully operative condition, predetel mined maximum reading will be obtained upon meter A. However, if the detector coils I! aredefective,'as, for instance, by having several turns shorted, or by being completely shorted, or if the ci'rcuit through the coils is completely broken. then the reading on meter A will be either reduced to a corresponding degree, or will slowly increase from the normal D. C. plate current reading to the reading corresponding to the open grid potential assumed by the grid of the oscillator tube.

Since there are two pairs of coils in each search unit shown in the Fig. 1 form of the detector mechanism, a similar unit as just described will have to be provided for the other pair of coils within the detector carriage, including a second button similar to 54 within the car body. Similarly, since there is another detecting mechanism cooperating with the other rail, additional test-- ing means similar to that just described, will have to be provided for the search unit at the other side. If each individual coil is to be tested separately, then four such testing devices would have to be provided for each search unit and a total of eight for the two units at the two sides.

In Fig. 4. I have shown a form of my invention wherein a separate independent testing unit may be connected to each coil for testing the same. This obviates the necessity of building the detector coils i2 with an auxiliary coil 3| permanently mounted adjacent thereto. In this form of the invention the auxiliary coil 3| is contained in a movable-unit 60, which is carried at the end of conductors 6| and 62 and may be connected to For this purpose each coil I2 is. shown as provided with open connections 63 which may extend into the ends of the cylinders in which said coils are mounted. The unit 60 is'provided with connections 84 adapted to engage the connections 63, and when said engagement is effected, auxiliary coil 3| is in inductive relation with respect to the J detector coil l2 which is being tested. The opermust be removed from the detector coils, and Y ation thereafter is as already described in connection with Fig. 2.

In Figs. 5 and 6 I'have disclosed a modified form of my invention. Instead of incorporating the contacts 64in the same member 60,-which carries theauxiliary coil 3|, I may provide a sep,-- ara-te lead line 10, carrying contacts 64, adapted to engage contacts 63',- which in this instance are housed in the upper portion oi-the detector carriage frame l3. Theauxiliary coil 3| is contained within the member said member having a concave surface adapted to fit beneath the cylinder which hduses the detector coil to be tested, so that when housing 60' is in position the auxiliary coil 3| and the' detector coil l2 to be tested are in inductive relation to complete the oscillatory circuit. Both in Fig. 2 and Fig. 6 the testing unit may be contained in a separate in-- strument case H, which is portable, and carries the leads I0 and 12, which may be connected as described to the search unit when a test is 'to be made. In the diagram of Fig. 5 I have disclosed certain additional features which may be applied to the wiring diagram of Fig. 2. These include a 'stop or button 80, which upon being depressed will short-circuit the detector coil l2 in order that a predetermined value of D. C. plate current may be established and observed upon meter A,

either when the'circuits are in position to allow ama'res A said coils 3i and 3| and their cores u, w are oscillation or under non-oscillatory'or partially oscillatory conditions. It will be understood that this is necessary because when the oscillatory circult is established between the detector coil i2 5 and the auxiliary coil ii, the current flowing through meter A is the sum of the plate current plus the average current due to the oscillation.

. Inaddition I have provided a means in Fig. 5

whereby the resistance between the grid and illament, that is, between points and 16, may

remain constant in spite of rheostat adjustment to maintain a fixed voltage on the grid 42. Thus, for instance, the voltage for said grid maybe supplied from battery BI and said voltage may be 15 controlled through a potentiometer comprising resistance 82 andsliding contact 83. As the contact 83 is moved along the potentiometer to control the yoltage applied to the grid, it will be seen that a variation in resistance is set upbetween points 15 and IS in the oscillatory circuit because the path of oscillation extends Irompoint 15 along the arrows to point 16. As contact '83 is moved to the right or left in said figure, the porition of the potentiometer contained in the oscillatory circuit between contact I! and point, O l, is increased or decreased correspondingly. To oilset the portion of resistance thus introduced, I incorporate a second resistor 85, with whichw a contactlS' integral with contact 83 engages. It will now be seen that as the-resistancebetween points 83 and 84 increases or decreases the resistance between points 83' and 8| decreases or increases respectively'to compensate for the 'variation in resistance which would ordinarily be introduced and thus leaves the resistance between points I5 and 16 substantially constant.

Another method of compensating for the-variations in resistance described above is shown in Fig.8. In this form of the invention a condenser 40 95 of large capacityis connected around-the variable resistance 82, 83. The capacity oi this condenser isso large that the reactance between points 04 andio is negligible at oscillatoryfrequency and variations in resistance 82 are no .45 factor because the condenser oilers a low im-,

pedance by-pass. I

- In Fig. 7 I have disclosed still another modification of my invention. This form mayoperate upon either or two principles. I employ within the testing unit two auxiliary colla and ii. 33! one method of operation of this form 01' my invention the testing coils ii and ,3! are so posi;

. tioned relative to eachpther that no oscillation is a normally set up between them although said coils bear to each other somewhat the same relation as -coil II bore to the detector coil I! in the other forms of the invention. No oscillation is set up, however, because the degree of coupling is controlledby increasing the reluctance of the masg9 netic circuit between them. Thus I have shown said coils provided with iron cores ll, ll, which form together an incomplete magnetic circuit. When. however. the testing unit comprising-the brought into testing relation with detector coil II, the core 30 of said. coil completes the magnetic circuit through the cores ll, thus decreasing v the reluctance of said circuit and causing an oscillation to be set up. In' this case, also, the degree of oscillation as compared with a predetermined degree oi"oscillation caused by a perfect detector coil, gives an indication of the conoscillation but to modify the'same in accordance with the conditionof the detector coil.

In accordance with the provisions of the patent statutes. I have herein described the principle and operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereoLbut I desire to have it understood that the apparatus shown is only illusftrative and that the invention can be carried out.

'by other means. -Also, while it is designed to use the various features and elements in the combinationand relations described, some of these may be altered and others omitted without intertering with the more general results outlined, and the invention extends to suchuse.

Having described my invention, what I clai and desire to secure by Letters Patent is: 1. A device for investigating the condition oi detector coils in a flaw detector mechanism, said I mechanism including a detector circuit in which said coils are-normally connected, an oscillatory circuit in which said coils are, adapted-to be connected, means whereby said coils may be disconnected from said detector circuit and connected into said osciilatorycircuii; when said coils are to be tested, and means for measuring the current in said oscillatory circuit. 2. A device for investigating the condition '01 detector coils in a flaw detector mechanism ,adapted to be mounted beneath a flaw detector cult in which said coils are adapted to be connected, an oscillatory circuit in which said coils are adapted to be connected, and means operatable ear, 'saidTmechanism including a detector clrfrom within the car for selectively rendering said circuits eirective.

3. A device for investigating the condition of 4 moans a. on. V 

